Turbo-electric furnace

ABSTRACT

An electrically powered furnace consisting of an elongated housing having an air intake assembly at its forward end and a discharge duct at its rear end leading to a hot air distribution system. A motor-driven air impeller assembly is provided in the intermediate portion of the housing. A first multiple-turn spirally coiled heating element is mounted in the forward portion of the housing between the impeller assembly and the air intake assembly. A second multiple-turn spirally coiled heating element is mounted in the rear portion of the housing between the impeller assembly and the discharge duct. A rotatable suction vane assembly is provided in the discharge duct. to provide smooth flow from the housing and accompanying smooth distribution of the heated air therein.

United States Patent [72] Inventor Fred Sanders 1,996,927 4/1935 Lake 165/122 50 E 0 h l l n hi 4 108 2,096,023 10/1937 Albertson 219/370 x 1 1 pp 12.068 2,153,239 4/1939 Curci 219/368 Filed 17,1970 2,428,079 9 1947 Hooper 219/370 x Patented 3 19 1 2,478,559 8/1949 Bergeron. 219/369 2,583,526 l/1952 Gaudette 219/366 X 54 TURBO-ELECTRIC FURNACE Primary Examiner-A Harris 12 claims, 5 Drawing Figs Attorney-Herman, Davidson and Berman [52] HS. Cl 219/369,

165/122, 219/360, 219/368, 2 l 9/374, 2 l9/376 ABSTRACT: An electrically powered furnace consisting of an [51] Int. Cl F24h 3/04, elongated housing having an air intake assembly at its forward end and a discharge duct at its rear end leading to a hot air dis- 0' Search [ribution system A moto udriyen air impeller assembly is pro 373-3761379482, vided in the intermediate portion of the housing. A first multi- 122 ple-turn spirally coiled heating element is mounted in the forward portion of the housing between the impeller assembly [56] Reterences cued and the air intake assembly. A second multiple-turn spirally UNITED STATES PATENTS coiled heating element is mounted in the rear portion of the 896,554 8/1908 Kyle 219/374 X housing between the impeller assembly and the discharge 1,368,328 2/1921 Eaton 219/376 X duct. A rotatable suction vane assembly is provided in the 1,509,367 9/1924 Miller 219/374 X ischarge duct. to provide smooth flow from the housing and accompanying smooth distribution of the heated air therein.

PATENIEMuvsom: v 3624.350

sum 3 0F 4 PIC-5'. G

INVENTOR. F 1950 E. s/lwozes i fimmfk wu,

TURBO-ELECTRIC FURNACE This invention relates to furnaces, and more particularly to an electrically energized hot air furnace of the type including blower means.

The main object of the invention is to provide a novel and improved electrically energized hot air furnace which is relatively simple in construction, which is very compact in size, and which provides efficient utilization of input energy.

A further object of the invention is to provide an improved electrically energized hot air furnace of the blower type, said furnace being inexpensive to fabricate, being durable in construction, requiring a minimum amount of maintenance attention, and providing efiicient distribution of heated air to the system associated therewith. v

A still further object of the invention is to provide an improved electrically energized hot air furnace of the type incorporating a turbine assembly therein to propel air therethrough, the assembly involving relatively inexpensive components, providing efficient transfer of energy, being quiet in operation, being easy to clean and having a high air distribution capacity.

A still further object of the invention is to provide an improved hot air furnace which compares favorably and is competitive with conventional gas furnaces such as the type employed in the majority of dwellings in the United States at the present time.

A still further object of the invention is to provide an improved electrically operated hot air furnace system employing a deodorant screen, the system being convertible to use as an air distributing and ventilating system in warm weather, under which conditions the deodorant screen may be removed.

A still further object of the invention is to provide an improved electrically energized hot air furnace assembly which may be employed at times as an air-distributing means, for example, to provide a flow of cool air in a house in warm weather, under which conditions, the heating elements of the furnace are deenergized and the turbine blade elements of the furnace may be driven at a suitable relatively slow rate of speed.

A still further object of the invention is to provide an improved electrically energized hot air furnace wherein heat loss from the furnace is held to a low value by the provision of a heat shield on the furnace unit, said heat shield being of efficient construction, being easy to install, and being of compact design.

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

FIG. I. is a front end view of an improved electrically energized hot air furnace constructed in accordance with the present invention.

FIG. 2 is a side elevational view of the furnace of FIG. 1.

FIG. 3A-3B is a longitudinal cross-sectional view taken, through the furnace substantially on the line 33-of FIG. 1, shown in two parts for convenience of illustration.

FIG. 4 is an enlarged transverse vertical cross-sectional view taken substantially onthe line 4-4 of FIG. 2.

FIG. 5 is an enlarged transverse vertical cross-sectional view taken substantially on the line 5-5 of FIG. 2.

FIG. 6 is an enlarged transverse cross-sectional view taken substantially on the line 6-6 of FIG. 2.

FIG. 7 is an enlarged transverse vertical cross-sectional view taken substantially on the line 7-7 of FIG. 2.

FIG. 8 is a side elevational view of an electric furnace provided with a heat shield, in accordance with the present invention.

FIG. 9 is a transverse vertical cross-sectional view taken substantially on the line 9-9 of FIG. 8.

FIG. 10 is a cross-sectional view of the heat shield element of FIG. 9 with said elements shown separated from the furnace housing.

FIG. 11 is an enlarged fragmentary cross-sectional detail view taken substantially on the line 11--1l of FIG. 8.

FIG. 12 is an enlarged fragmentary cross-sectional view taken substantially on the line 12-12 of FIG. 8.

FIG. 13 is an enlarged fragmentary perspective view, partly in cross section, showing a pair of interengageable heat shield segments as employed in FIG. 8, with the segments separated and showing the interengaging lug and socket elements of the segments.

FIG. 14 is an enlarged fragmentary cross-sectional detail view taken substantially on the line 14-14 of FIG. 8.

Referring to the drawings, 11 generally designates an improved electrically energized furnace assembly constructed in accordance with the present invention. The assembly ll comprises an elongated housing 12 which may have any desirable crosssectional shape, for example, it may be of circular crosssectional shape as illustrated in the drawings merely by way of example. The housing 12 is provided at its forward end with an air intake assembly designated generally at 13 and is provided at its rear end with a discharge duct 14 leading to a conventional hot air distribution system, illustrated in FIG. 2 as including the respective air distributing branch conduits 15. It will be further noted that the rear end portion of the housing 12 tapers in cross section, as shown at 16, providing a substantial reduction in cross section between the main portion of the housing and the outlet end thereof.

The elongated housing 12 is mounted on and supported by a rigid frame structure comprising a flat hollow horizontal base 17 and an upstanding boxlike frame 18 defining a compartment 19 beneath the intermediate portion of the elongated main housing above. Mounted in the compartment 19 on an axis parallel to the main housing 12 is a motor-generator set comprising the electric motor 20 and the generator 21 driven thereby. The generator 21 is employed as the source of heater voltage for the unit, as will be presently described. The housing 18 is provided with a conventional power input receptacle 23 adapted to receive the female socket portion 24 of a conventional power supply line cord 25.

The walls of the framelike supporting housing 18 are suitably apertured to provide ventilation therethrough, as shown at 26, and the flat horizontal hollow base is likewise provided with an adequate number of apertures to ensure proper ventilation thereof.

The air intake assembly 13 comprises a relatively large dishshaped hood member 27 secured on the front end of the elongated housing 12 coaxially therewith, as shown in FIG. 3, the forward end of the main housing 12 being provided with a first annular forwardly flaring throat portion 28 and a second forwardly spaced annular inlet conduit 29 comprising a forwardly flaring front portion 30 and a cylindrical portion 31 arranged coaxially within the flaring throat 28, as shown, in FIG. 3. This arrangement defines a plurality of air inlet paths leading to the intake end of the main housing 12, one of said paths being the annular space 32 defined between the members 28 and 29 and the other path being that defined by the inner conduit 29. The member 29 is suitably supported, for example, by radial struts 33 connecting the cylindrical portion 31 to the forwardly flaring front end portion 28 of main housing 12. The dish-shaped member 27 is rigidly supported by longitudinally extending bracket arms 34 connected to the forwardly flaring conduit I portion 30, as well as by bracket arms 35 connecting the skirt portion of member 27 to the forwardly flaring front end portion 28 of main housing 12.

An annular screen 36 is provided in the intake space between the rim of member 27 and flaring portion 28, as shown in FIG. 3. A deodorant screen 37 is removably mounted in the member 27 forwardly of and coaxially with the central intake conduit member 29. The deodorant screen 37 may comprise any suitable material impregnated with conventional deodorant, acting to cleanse the air flowing adjacent thereto. As will be apparent from FIG. 3, the arrangement within the air intake assembly 13 such that the major portion of the air entering same flows toward the center portion thereof in a path causing the major portion of the air to flow pass the deodorant screen 37 into the inner conduit 29.

The intermediate portion of the main housing 12 contains an air impeller assembly comprising a series of spaced transverse stationary turbine vane assemblies 39 rigidly mounted in main housing 12 through the center portions of which rotatably extends a turbine shaft 40 carrying the rotor blade assemblies 41 interleaved with the stationary blade assemblies 39. The front end of shaft 40 is joumaled at 42 in a rigid supporting member 43 secured diametrically in the main housing 12, and the rear end of shaft 40 is similarly journaled at 44 in a rigidly secured diametrically extending support member 45 secured in main housing 12, as shown in FIG. 3. The shaft 40 has a reduced rear extension 46 extending axially through the tapered outlet portion of the main housing, the rodlike shaft extension 26 being rigidly connected centrally to a turbinelike suction disc assembly 47 joumaled in the throat portion 48 defined at the end of the tapered outlet 16 of main housing I2. It will thus be apparent that the suction disc assembly 47 rotates at the same rate as the main turbine blade assemblies 41 and acts to provide smoother control of the compressed heated air flowing through the convergent housing outlet portion 16 by reducing the effects of friction and turbulence in this portion of the system.

A first air-heating assembly, designated generally at 50, is mounted in the forward portion of the elongated tubular housing I2, namely, between the air intake assembly and the air impeller assembly. The air-heating assembly 50 comprises a plurality of spirally coiled electrical heating elements 51, secured in spaced parallel coaxial arrangement in the forward portion of housing 12, as is clearly shown in FIG. 3. The heating elements 51 are energized by the generator 21, being connected to the output thereof in any suitable manner. Thus, the output of generator 21 may be connected to the heating elements 51 through a conventional voltage regulator 52.

An additional air heating assembly, designated generally at 54, is mounted in the rear portion of housing 12, namely, between the air impeller assembly and the air discharge throat 48, as shown in FIG. 3. The rear air-heating assembly 54 comprises a succession of parallel spirally coiled electric heating elements 55, generally similar to the heating elements 51, and secured together in spaced parallel relationship coaxially in the housing 12, as is clearly shown in FIG. 3. The rear air-heating assembly 54 is also energized from the generator 21, the output of said generator being connected to the heating elements 55 through the voltage regulator 52.

The heating elements 51 in the forward portion of the hous ing and the heating elements 55 in the rear portion of the housing are rigidly secured therein in any suitable manner, for example, may be supported in longitudinally extending notched ribs 57 and 58 of suitable refractory material secured to the inside surface of housing 12, and the turns of the heating elements may be braced so as to remain in parallelism by the use of auxiliary brace bars of similar refractory material, if so desired.

The shaft of the motor generator set, shown at 59, is provided with an output pulley 60 which is drivingly coupled by a belt 61 to a pulley 62 provided on the shaft 40 of the impeller vane assemblies 39. As shown in FIG. 3, the belt 61 extends through suitable slots or apertures 63 provided in the bottom wall portion of housing 12, as viewed in FIG. 3. Thus, energization of the motor simultaneously drives the impeller shaft 40 and the generator 21, causing the heating elements 51 and 55 to be energized at the same time that the rotary impeller vane assembly 39 and the suction disc assembly 47 are driven.

As shown in FIG. 7, the suction disc assembly 47 comprises a plurality of impeller vanes mounted in a supporting ring 70 which is joumaled in the housing throat portion 48 by means of an annular ball bearing assembly 71, allowing the ring 70 to rotate freely in the throat 48, carrying the vanes on the disc assembly 47 therewith.

In operation, with the motor 20 energized, as above mentioned, air is drawn into the intake assembly 13 through the screen 36, some of the air passing through the annular intake passage 32 and the major portion of the air flowing past the deodorant pad 37 into the intake duct 29. The draft provided by the rotating impeller vane assemblies 39 moves the air through the electrical heating assembly 50, raising the temperature of the air as it moves through the forward portion of housing 12 toward the right, as viewed in FIG. 3. The heated air is then drawn through the stationary and rotating impeller vanes, providing a substantial buildup of pressure of the air as it passes into the rear portion of housing 12, namely, the portion containing the relatively large number of electrical heating elements 55. The buildup of pressure in this portion of the housing 12, as well as the effect of the heating elements 55, greatly increases the temperature of the air. The relatively high pressure, high temperature air is then forced into the distributing conduit 14 through the suction vane assembly 47 for distribution to the various discharge ducts I5.

It will be noted that the spirally coiled heating elements 55 contained in the rear portion of the elongated housing 12 are substantially greater in number than the spirally coiled heating elements 51 contained in the forward portion of the housing, whereby a major portion of the heat transmission to the air occurs after it has been moved through the main blower means defined by the alternating stationary and rotary turbine vane assemblies 39 and 41. Thus, major heat input to the air occurs at the same time as the pressure is built up in the rear portion of the housing, the buildup in pressure taking place because of the reduction in cross-sectional area at the throat portion 48. The proportion of heat input to the air, as between that which occurs ahead of the main blower assembly and immediately to the rear thereof may be varied in accordance with the requirements of particular installations and in accordance with the type of ambient conditions to be encountered. However, in general, the number of rear heating elements 55 will be substantially greater than the number of forward heating elements 51.

It is also apparent from FIG. 3 that the spacing of the heating elements 55 is relatively close as compared with the spacing of the heating elements 51. This spacing is also a design factor, depending upon the available length of housing for the desired number of heating elements to be employed, and in accordance with the rate at which heat is to be delivered to the moving air. It will be readily apparent that it is desirable to employ a large number of rear heating elements 55 because this provides for a correspondingly greater heat input to the air forced through these heating elements from the main blower assembly, making it possible to deliver a massive amount of heat to this air while its pressure is being built up in the rear portion of housing 12. The buildup of pressure also causes temperature rise of the air, so that the two effects combine to provide a very large heat capacity for a unit of modest size.

In order to prevent excessive heat loss from the heat-shield it is desirable to provide suitable heat-shield means on the furnace unit. FIGS. 8 to 14 show a typical form of heat shield means which may be employed with the furnace. To facilitate the installation of the heat-shield means it is preferably made in sections, with the provision of suitable interengaging locking means to hold the sections in place on the furnace housing 12. Thus, as shown in FIG. 8, the heat-shield means consists of a group of center segments including a bottom segment 72, front and rear segments 73 and a top segment 74. The forward group of heat-shield segments similarly consist of a bottom segment 75, front and rear segments 76 and a top segment 77. The rear group of heat-shield segments consists of a bottom segment 78, front and rear segments 79 and a top segment 80.

The various heat-shield segments 72 to 80 are of generally similar construction and are conformably shaped in accordance with the portions of housing 12 on which they are mounted. For example, as shown in FIG. 14, the segment 73 comprises a sheet metal arcuately curved outer plate 83 provided with an inside lining 84 of suitable heat-insulating material, such as fiber glass composition, or the like. The layers 84 and 83 are secured to a ventilated ring segment 85,

for example, by fastening screws 86 shown in FIG. 14. The ring segment 85 is aligned with similar ring segments 87 and 88 provided on the adjacent heat-shield segments 72 and 74, as shown in FIG. 8. The ventilated ring segments engage on and are shaped conforrnably with the outer surface of housing 12, and act to support the layers 84 and 83 in spaced relationship through the housing 12 so as to define an air space 89 externally adjacent the housing 12, as shown in FIG. 14.

The front group of heat-shield segments 75, 76 and 77 are similarly provided with ventilated support ring segments 90, 91 and 92, similar in construction to segments 85, 87 and 88, and being secured in the same manner to the outer layers of the respective segments 75, 76 and 77 as described above and as illustrated in FIG. 14. The bottom heat-shield segments 75 and 78 are secured to the underside of the main housing 12 by sheet metal screws 93, with the middle bottom segments 72 in terlocked therebetween and clamped thereto by suitable toggle clamps 94, having the structure illustrated in FIG. 11.

The heat-shield segments of the various groups are interlockingly engaged at their longitudinal edges by the provision of locking projection 96 on said longitudinal edges which are receivable in conformably shaped recesses or sockets 97 provided in the edges of the adjacent segments, as shown in FIGS. 12 and 13. As above mentioned, the segments are interconnected at their ends by clamp assemblies 94. For example, as shown in FIG. 11, the right end of the segment 73 is provided with an upturned hook-shaped locking rib element 98 which is lockingly engageable by the clamping hook 99 of a pivoted clamping toggle arm 100 provided on the adjacent margin of the heat-shield segment 76. The clamping assemblies 94 are similar to those commonly employed, for example, in fastening covers of luggage or other receptacles. The heat-shield segments are therefore clampingly secured together at their adjacent ends, while at the same time being interlocked at their longitudinal edges. As will be readily understood, this makes it relatively easy to remove the heat-shield segments whenever necessary and to quickly replace said segments, if so desired.

As shown in FIG. 8, the middle bottom segment 72 is suitably apertured to provide clearance for the upstanding boxlike frame 18.

During the operation of the furnace unit, the heated air in the jacket space 89 is drawn into the air intake assembly 13 by the suction induced in the intake assembly by the action of the inwardly flowing air, whereby the otherwise wasted heat is returned to the system. Thus, any heated air moving along the surface of the main housing 12 will flow through the jacket 89 and will be drawn into the intake assembly 13.

The furnace unit may be employed as a ventilating and cooling means for the building in which it is installed, for example, in warm weather, by decnergizing the heating elements and operating the rotor blade assemblies at a relatively slow speed. Thus, suitable speed-control means may be provided for the motor 20, as well as suitable switch means for disconnecting the generator 21 from the heating elements at times for the purpose above described. The motor-speed control means may be of any conventional type, enabling the speed of the motor to be controlled, whereby the turbine blades may be driven at relatively slow speed in warm weather for air-circulation purposes, or may be driven at a desired relatively rapid rate of speed so as to provide the desired air-compression effects cooperation with the heating elements as described above when the apparatus is operated as an air-heating furnace in cold weather.

Suitable control means may be provided for regulating the degree of energization of the heating elements 51 and 55. Thus, such control means may be of conventional construction, for example, similar to those provided on ordinary electric cooking ranges.

It will be readily apparent, that the above-described furnace assembly, when operated properly, will provide high efficiency and will operate with economy comparable to and in some cases superior to that of the conventional gas furnace employed in a majority ofdwellings.

The deodorant screen 37 is readily removable and can be easily removed when the apparatus is employed as an air-circulating and cooling device under warm weather conditions, with the heating elements 51 and 55 deenergized.

It will be noted that the heat-shield assembly, illustrated in FIGS. 8 to 14, is relatively small in radial thickness, as compared with the air intake assembly 13, and thus does not in any way interfere with the intake of air into the furnace.

While a specific embodiment of an improved electrically powered hot air furnace has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention may occur to those skilled in the art. Therefore, it is intended that no limitations be placed on the invention except as defined by the appended claims.

lclaim:

l. A hot air furnace assembly comprising an elongate generally tubular housing, air intake means at one end of the housing, outlet conduit means at the other end of the housing adapted to be connected to an air distribution system, air blower means mounted in the intermediate portion of the housing, a first electrical air heating unit including a plurality of spaced parallel substantially spirally coiled electrical heating elements mounted in the housing between said air intake means and said air blower means, a second electrical air-heating unit including a plurality of spaced parallel substantially spirally coiled electrical heating elements mounted in the housing between the air blower means and the outlet conduit means, suction blower means mounted in said outlet conduit means, means including a common drive shaft to synchronously drive said air blower means and suction blower means, said air blower means comprising a series of alternately stationary and rotary turbine vane assemblies transversely located in said housing, said common drive shaft being centrally and drivingly connected to said rotary turbine vane assemblies, said housing converging in cross-sectional area toward said outlet conduit means, defining a throat portion at the connection to said outlet conduit means, said suction blower means being located in said throat portion, said suction blower means comprising a rotary turbine vane assembly journaled in said throat portion, said air intake means comprising a substantially dish-shaped hood member receiving but spaced from one end of the housing, defining an annular air intake passage therebetween for air to flow into the hood member and thence into the said one end of the housing, said one end being provided with an outwardly flaring rim which is substantially received in said hood member, and said annular intake passage being defined between said rim and the peripheral margin of the hood member.

2. The hot air furnace assembly of claim 1, and a central annular intake conduit member mounted coaxially in said rim and having an outwardly flaring forward portion spaced forwardly from said rim and being located in the interior of said hood member and being spaced therefrom to define a further annular air intake passage leading into said annular conduit member.

3. The hot air furnace assembly of claim 2, and air deodorizing means mounted substantially centrally in said hood member adjacent said outwardly flaring forward portion of the annular intake conduit member.

4. The hot air furnace assembly of claim 3, and a driving motor mounted adjacent the housing, and drive belt means coupling said motor to said common drive shaft.

5. The hot air furnace assembly of claim 4, and heat-shield means mounted on said tubular housing substantially coextensive therewith and being spaced therefrom to define an air jacket externally adjacent said housing.

6. The hot air furnace assembly of claim 5, and wherein said heat-shield means extends into saidhood member, whereby said air jacket communicates with the interior of the hood member.

7. The hot air furnace assembly of claim 6, and wherein said heat-shield means comprises a plurality of interlocking segments conforming in contour with the housing and provided with means to clampingly secure the adjacent segments together in endwise abutting relationship.

8. The hot air furnace assembly of claim 7, and wherein each heat-shield segment isprovided with an apertured inwardly extending abutment element engageable with the housing so as to space the segments from the housing and so as to define said air jacket.

9. The hot air furnace assembly of claim 1, and heat-shield means mounted on said tubular housing substantially coextensive therewith and being spaced therefrom to define an air jacket externally adjacent said housing.

10. The hot air furnace assembly of claim 9, and wherein said heat-shield means extends into said hood member, whereby said air jacket communicates with the interior of the 

1. A hot air furnace assembly comprising an elongate generally tubular housing, air intake means at one end of the housing, outlet conduit means at the other end of the housing adapted to be connected to an air distribution system, air blower means mounted in the intermediate portion of the housing, a first electrical air heating unit including a plurality of spaced parallel substantially spirally coiled electrical heating elements mounted in the housing between said air intake means and said air blower means, a second electrical air-heating unit including a plurality of spaced parallel substantially spirally coilEd electrical heating elements mounted in the housing between the air blower means and the outlet conduit means, suction blower means mounted in said outlet conduit means, means including a common drive shaft to synchronously drive said air blower means and suction blower means, said air blower means comprising a series of alternately stationary and rotary turbine vane assemblies transversely located in said housing, said common drive shaft being centrally and drivingly connected to said rotary turbine vane assemblies, said housing converging in crosssectional area toward said outlet conduit means, defining a throat portion at the connection to said outlet conduit means, said suction blower means being located in said throat portion, said suction blower means comprising a rotary turbine vane assembly journaled in said throat portion, said air intake means comprising a substantially dish-shaped hood member receiving but spaced from one end of the housing, defining an annular air intake passage therebetween for air to flow into the hood member and thence into the said one end of the housing, said one end being provided with an outwardly flaring rim which is substantially received in said hood member, and said annular intake passage being defined between said rim and the peripheral margin of the hood member.
 2. The hot air furnace assembly of claim 1, and a central annular intake conduit member mounted coaxially in said rim and having an outwardly flaring forward portion spaced forwardly from said rim and being located in the interior of said hood member and being spaced therefrom to define a further annular air intake passage leading into said annular conduit member.
 3. The hot air furnace assembly of claim 2, and air deodorizing means mounted substantially centrally in said hood member adjacent said outwardly flaring forward portion of the annular intake conduit member.
 4. The hot air furnace assembly of claim 3, and a driving motor mounted adjacent the housing, and drive belt means coupling said motor to said common drive shaft.
 5. The hot air furnace assembly of claim 4, and heat-shield means mounted on said tubular housing substantially coextensive therewith and being spaced therefrom to define an air jacket externally adjacent said housing.
 6. The hot air furnace assembly of claim 5, and wherein said heat-shield means extends into said hood member, whereby said air jacket communicates with the interior of the hood member.
 7. The hot air furnace assembly of claim 6, and wherein said heat-shield means comprises a plurality of interlocking segments conforming in contour with the housing and provided with means to clampingly secure the adjacent segments together in endwise abutting relationship.
 8. The hot air furnace assembly of claim 7, and wherein each heat-shield segment is provided with an apertured inwardly extending abutment element engageable with the housing so as to space the segments from the housing and so as to define said air jacket.
 9. The hot air furnace assembly of claim 1, and heat-shield means mounted on said tubular housing substantially coextensive therewith and being spaced therefrom to define an air jacket externally adjacent said housing.
 10. The hot air furnace assembly of claim 9, and wherein said heat-shield means extends into said hood member, whereby said air jacket communicates with the interior of the hood member.
 11. The hot air furnace assembly of claim 10, and wherein said heat-shield means comprises a plurality of interlocking segments conforming in contour with the housing and provided with means to clampingly secure the adjacent segments together in endwise abutting relationship.
 12. The hot air furnace assembly of claim 9, and wherein said heat-shield segment is provided with an apertured inwardly extending abutment element engageable with the housing so as to space the segments from the housing and so as to define said air jacket. 